Methylation of hemoglobin to enhance flocculant performance

Authors: ESSANDOH, MATTHEW - Orise Fellow; Garcia, Rafael; Strahan, Gary

Submitted to: Journal of Chemical Technology & Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2016
Publication Date: 2/14/2017
Citation: Essandoh, M., Garcia, R.A., Strahan, G.D. 2017. Methylation of hemoglobin to enhance flocculant performance. Journal of Chemical Technology & Biotechnology. doi: 10.1002/jctb.5197.

Interpretive Summary: Water that is contaminated with suspended solids is typically treated with substances called flocculants to remove the solids and clarify the water. Currently, many of the flocculants used are synthetic polymer flocculants (SPF). These SPF, especially one known as polyacrylamide (PAM), are made up of chemicals that are very harmful and are capable of causing cancer. Regulatory agencies and consumers are therefore calling for safe, renewable substitutes for SPF. Hemoglobin is a component of blood, and it can be obtained inexpensively from waste slaughterhouse blood. Past research has shown that hemoglobin has many of the properties of SPF. One drawback of hemoglobin is that it works well only if the contaminated water is acidic. In this research, a simple chemical reaction was used to modify hemoglobin; the modification was anticipated to improve the flocculant performance of hemoglobin under less acidic conditions. Experiments compared normal and modified hemoglobin in terms how well they clarify water, and the dose required to achieve good clarification. The results show that the modification had the desired effect of improving performance in water that is near neutral pH. The modification also had the unexpected effect significantly improving overall flocculant performance; under some conditions, the modified hemoglobin could clarify water as well as regular hemoglobin with only one quarter the dose. This research has provided a simple, inexpensive way to improve the performance of a hemoglobin-based flocculant. Such an improvement will expand the opportunities for commercial application of the flocculant.

Technical Abstract: An inexpensive bioflocculant, bovine hemoglobin (Hb), has been covalently modified through methylation of the side chain carboxyl groups of aspartic and glutamic acid residues to improve its flocculation activity. Potentiometric titration of the recovered products showed approximately 28% degree of methylation when the Hb was suspended in methanol with 0.8M HCl for 48 h. Nuclear magnetic resonance spectroscopy, Fourier Transform-Infrared spectroscopy, and circular dichroism analyses were used to characterize the effects of methylation on the Hb molecule. The alpha helix content decreased from 61% in Hb to 8% in the methylated hemoglobin (MeHb). Flocculation experiments were carried out for both Hb and MeHb under different experimental conditions (settling time, solution pH, and flocculant doses). Methylation resulted in improved flocculation performance. Under some conditions, MeHb clarified suspensions of kaolin at ¼ the dose that was required for Hb. Further, MeHb exhibited flocculant activity over a wide pH range, compared to Hb.